Poly(amino acids) such as poly(aspartic acid) are useful as additives for fertilizers, scale inhibitors, detergents, pigment and mineral dispersants, and corrosion and scale inhibitors in boilers and cooling towers. Poly(amino acids) have been synthesized by hydrolyzing the products of thermal polycondensation reactions of amino acids. Unfortunately, the known methods for the synthesis of poly(amino acids) are complex, expensive, or require excessively long process times.
A method for the synthesis of poly(aspartic acid) is disclosed in U.S. Pat. No. 4,839,461 to Boehmke. This process combines maleic acid or maleic anhydride and an ammonia solution in a molar ratio of 1:1-1.5. The mixture is then heated to 120.degree.-150.degree. C. and the resulting solution of ammonium salt and maleic acid is evaporated, leaving a crystal mash. The crystal mash is then melted, during which time the waters of condensation and crystallization distill off. A porous mass of poly(aspartic acid) results. The entire process requires six to eight hours to complete.
Another method for the synthesis of poly(amino acid) is disclosed in U.S. Pat. No. 5,057,597 to Koskan, et al. This process requires fluidizing an amino acid by agitation in a nitrogen atmosphere at a temperature of at least 180.degree. C. for three to six hours. The resultant anhydropolyamino acid is then hydrolyzed to a poly(amino acid).
The prior art methods for the synthesis of polysuccinimides and poly(amino acids) are time consuming, complex or use large volumes of volatile organic solvents or inert gases. As used hereinafter and in the appended claims, "polysuccinimides" refers to polymeric materials which contain succinimide moieties in the polymer chain and may contain other moieties, and "polysuccinimide" refers to polymeric materials which contain only such moieties.
It is an object of this invention to provide a relatively simple process for the manufacture of polysuccinimides which can then be hydrolyzed to form poly(amino acids).
It is a further object of the present invention to provide a continuous process for preparing polysuccinimides.